If the pack frame will not be load bearing, consider the best of the frameless or non-load bearing frame packs currently reviewed here.
If it will be load bearing, it is hard to get around the fact that construction material under 3/8" in diameter weighs much less than the larger diameter alu alloy tubing that has been used on most marketed packs and rucksacks. Even solid quarter inch FG rods are much lighter than the larger diameter alloy, as are the thick walled hollow FG tubes used for cheap tents; but FG will not hold a bend like alloy, of course, and the frame design must address that.
For the above reasons, lighter and lower diameter frame material is probably the only way forward, to achieve an SUL load bearing frame.
(Note that the "FSD Edge Connectors" in the 8mm (.312") size from Goodwinds might make great T connectors to replace the home-made ones crafted by Roger. They are friction fit, so require no adhesive or fasteners. The challenge is putting a slight uniform bend in the 8mm alloy tubing, without Roger's "rolling jenny" device. Tried a Ridgid 3/8" tube bender, but it leaves small crimps on the inside of the bend as you go along, bending just a little at successive points, which weakens the tubing.)
Will post on completion of current project using mostly 1/4" dia. FG and 8mm Easton .340" dia. alloy, and even small lengths of 1/4" solid alu (for two very low radius bends). The FG rod was chosen over carbon fiber, because it is much more flexible, still very strong, and not that much heavier for the same dia.(also much cheaper). The frame will be integral to the pack, and have sidearms to eliminate the full waist belt, a la Jack Stephenson's original go-pack, which used an additional connection to the hip belt at the small of the back to avoid the backward pull of the sidearm frames that have beoome obsolete.
I used an MYOG go-pack design for many years, and still find it much more comfortable than anything with a full waistbelt, and that includes for loads in the 20-30 lb. range. The challenge is to greatly reduce the weight of the frame structure, including foldable sidearms. Without that, no amount of pricey cutting edge fabric will achieve the lightest pack weight. When carrying a much lighter pack, the bomb proof constructed frames I used to make should not be needed.
Good luck to us both.